GB 8624 is China's mandatory national standard for classifying the burning behavior of building materials and products, assigning materials to classes A, B1, B2, and B3 based on rigorous fire performance testing. This technical guide explains the GB 8624-2012 classification system, the required test methods such as the Single Burning Item (SBI) test, sample requirements, and practical compliance considerations for manufacturers supplying the Chinese construction market.
Technical Overview
GB 8624, titled "Classification for Burning Behavior of Building Materials and Products," is the fundamental Chinese national standard used to evaluate and grade the fire performance of construction materials. The current edition, GB 8624-2012, replaced GB 8624-2006 and was technically aligned with the European classification standard EN 13501-1, enabling more consistent comparison between Chinese and European fire test data.
Under GB 8624-2012, building materials and products are classified into four major grades with seven sub-levels:
- Class A (A1, A2) – Non-combustible materials that contribute virtually no fire load.
- Class B1 (B, C) – Flame-retardant materials with limited contribution to fire growth.
- Class B2 (D, E) – Combustible materials with acceptable but measurable contribution to fire.
- Class B3 (F) – Highly flammable materials that fail to meet any of the above requirements.
In addition to the primary fire classification, materials receiving classes A2 through D may also carry additional classifications for smoke production (s1, s2, s3) and for flaming droplets or particles (d0, d1, d2). These classifications are determined through a combination of standardized test methods measuring heat release, flame spread, ignitability, smoke opacity, and combustion characteristics.
Testing Samples
The scope of GB 8624 covers a wide range of construction products. Sample preparation, orientation, and mounting must strictly follow the relevant test method standards, as these factors significantly influence test results.
Flat Wall and Ceiling Products
Interior and exterior wall panels, ceiling boards, sandwich panels, aluminum composite panels, and decorative finishes are tested as vertically mounted flat products. The Single Burning Item test requires a specimen package assembled in a standard frame with backing board and joints, simulating realistic end-use installation.
Thermal Insulation Materials
Products such as EPS, XPS, polyurethane foam, phenolic foam, rock wool, and glass wool are classified under GB 8624. Combustible foam insulations commonly target Class B1, while mineral wool products typically achieve Class A1 or A2.
Flooring Materials
Carpet, PVC flooring, laminate flooring, wood flooring, and rubber flooring follow a dedicated classification pathway using the radiant panel test, because flooring fire behavior differs fundamentally from vertically oriented products.
Tubular Insulation and Linear Products
Pipe insulation materials and similar linear products are tested with appropriate mounting configurations that reproduce their installed geometry, ensuring the classification reflects real application conditions.
Decorative Textiles and Membranes
Wall coverings, curtains, ceiling fabrics, and coated fabrics used in buildings may be evaluated under GB 8624, particularly when specified by fire safety design requirements in public assembly occupancies.
Sample Conditioning Requirements
Prior to testing, specimens must be conditioned to equilibrium at a temperature of 23 ± 2 °C and relative humidity of 50 ± 5%. Minimum conditioning periods are typically dictated by product thickness, and specimens must be tested within a defined timeframe after removal from the conditioning atmosphere.
Testing Items
The GB 8624 classification scheme relies on a defined set of measurable fire performance parameters, each produced by a specific standard test method:
- Non-combustibility – Determined by GB/T 5464, measuring mass loss, sustained flaming, and furnace temperature rise of specimens exposed to 750 °C in a furnace.
- Gross heat of combustion (PCS) – Determined by GB/T 14402 using an oxygen bomb calorimeter, quantifying the total energy released by complete combustion.
- Fire growth rate index (FIGRA) – Derived from the GB/T 20284 Single Burning Item test, measuring how quickly heat release accelerates.
- Total heat release (THR600s) – Cumulative heat released during the first 600 seconds of the SBI test.
- Lateral flame spread (LFS) – Visual assessment of flame propagation beyond the specimen edge in the SBI test.
- Smoke growth rate index (SMOGRA) and total smoke production (TSP600s) – Smoke generation parameters measured in the SBI test.
- Flame spread distance (Fs) and flaming droplets – Evaluated in the GB/T 8626 small flame ignitability test with a 15-second or 30-second flame application.
- Critical heat flux at extinguishment (CHF) – Measured by the GB/T 11785 radiant panel test for flooring classifications.
- Smoke toxicity – Assessed under GB/T 20285 where required by project specifications, evaluating hazardous gas generation from smoldering combustion.
Testing Methods
The classification route depends on the declared target class and the product category. Laboratories follow a decision-tree approach combining the test methods below.
Route to Class A1
Class A1 requires compliance with both GB/T 5464 non-combustibility criteria and GB/T 14402 gross heat of combustion limits. Materials passing both tests without exceeding defined thresholds for temperature rise, mass loss, and PCS achieve the highest classification.
Route to Class A2
Class A2 requires the GB/T 20284 SBI test combined with either GB/T 5464 or GB/T 14402, plus GB/T 8626 ignitability verification. FIGRA, THR600s, SMOGRA, and TSP600s limits are slightly less stringent than A1, but sustained flaming criteria still apply.
Route to Classes B and C (B1)
Classes B and C, both corresponding to the B1 grade, are based on the SBI test with progressively relaxed FIGRA and THR600s thresholds, together with the GB/T 8626 small flame test. For class B, flame spread within 150 seconds must not reach a defined height; flaming droplets restrictions also apply.
Route to Classes D and E (B2)
Class D requires the SBI test with higher heat release limits, while class E requires only the GB/T 8626 small flame test, where flame spread must not exceed 150 mm within the observation period after flame application.
Route to Class F (B3)
Materials that fail the class E criteria are classified as F (B3) and are prohibited or heavily restricted in most building applications under Chinese fire codes.
Flooring Classification Route
Floor coverings are classified using GB/T 11785 radiant panel CHF values combined with GB/T 8626 ignitability results, with threshold CHF values mapped to classes A2fl through Efl. The "fl" suffix denotes flooring-specific classifications.
Applications
GB 8624 classification reports and certificates serve multiple critical purposes across the construction and manufacturing industries:
- Building code compliance – GB 50016, the Code for Fire Protection Design of Buildings, mandates minimum GB 8624 classes for materials used in specific locations such as evacuation routes, high-rise buildings, and crowded venues.
- Market access in China – Foreign manufacturers exporting construction products to China must demonstrate GB 8624 compliance through testing at accredited laboratories.
- Tender and procurement documentation – Government projects and large commercial developments routinely require B1 or A class certification for insulation and finish materials.
- Product development – Manufacturers use classification testing to verify flame-retardant formulations, optimize material thickness, and support additive or recipe changes.
- Fire safety assessment – Fire engineers and approval authorities rely on GB 8624 grades as objective inputs for performance-based fire safety design.
- Quality control – Periodic retesting supports factory production control and maintains the validity of classification claims for ongoing production.
FAQ
Which version of GB 8624 is currently in force?
GB 8624-2012 is the current version and has been mandatory since its implementation date. Test reports issued under GB 8624-2006 are no longer accepted for new compliance purposes, so manufacturers should ensure reports reference the 2012 edition.
What is the difference between GB 8624 and EN 13501-1?
The two standards are technically harmonized: GB 8624-2012 adopts classification levels and test logic closely aligned with EN 13501-1, and the underlying test methods are Chinese adoptions of corresponding ISO or EN standards. However, Chinese authorities require testing under the GB/T method standards, so EN test reports alone cannot substitute for GB 8624 classification.
How are the grades A, B1, B2, and B3 related to the sub-levels?
Class A includes sub-levels A1 and A2; B1 includes B and C; B2 includes D and E; and B3 corresponds to F. Procurement specifications in China commonly cite the broader grades (A, B1, B2, B3), while test reports state the precise sub-level.
How many samples are required for testing?
Sample quantities depend on the target class and product configuration. The SBI test typically requires multiple complete specimen packages, while GB/T 8626, GB/T 5464, and GB/T 14402 each require their own specimen sets. Laboratories usually provide a sampling plan listing exact dimensions, quantities, and mounting substrate requirements before testing begins.
How long does GB 8624 testing take?
Typical lead time ranges from three to eight weeks, depending on the classification route, whether multiple product variants are submitted, and whether any additional smoke toxicity testing is required.
Do cables fall under GB 8624?
No. Cables and wires are classified under a separate dedicated standard, GB 31247, which evaluates combustion performance, smoke density, and halogen acid gas emission. GB 8624 applies to building materials and construction products rather than electrical cables.
What do the additional classifications s and d mean?
The "s" classification (s1, s2, s3) ranks smoke production from low to high, while the "d" classification (d0, d1, d2) indicates the absence or presence and duration of flaming droplets and particles. For example, a complete result may read "B-s1, d0," which is essential information for materials installed in escape routes and large open spaces.
